On the Ginathodon beds around the head of Mobile Bay. 165 
the level of the sea. Others occur at Tromose and Drontheim, 
at an elevation of only five or six yards. 
Near the small town of Uddevalla, in Sweden, marine shells 
have been accumulated upon the shore to so great an extent, that 
from time immemorial they have been carted away for the pur- 
pose of paving the public ways. ‘These are at an elevation of 
about sixty yards; the shells are like those in the neighboring 
i sea; they are almost entirely exempt from earthy mixture. : 
Near Valparaiso in South America, about forty yards above the 
level of the ocean, there is a remarkable deposit consisting of a 
single species, the Concholepas, which is still living on the coast. 
hether the Gnathodon beds in question are to be classed 
with the preceding remains to be determined. 
Of the genus Gnathodon, there are two living species on the 
American coast, the Gnathodon cuneata and G. flexuosa, both 
occurring about the Gulf of Mexico. ‘These are estuary species, 
and inhabit brackish water : yet there are some apparent excep- 
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manner supposed. It was once thought that the Mytilus edulis 
Inhabited the Danube. But a more correct examination has since 
contended that no functional: change has been produced to render 
_ it permanently a fresh-water species. Jt is more than probable 
_ that the deposits far in the interior, are composed of individuals 
" that lived in the vicinity, and were coéval with the formation of 
as the sea retreated to its present limits at the head of Mobile bay, 
‘Here the species are yet found in circumstances congenial to 
their nature. An instance occurs in Maurepas lake where recent 
